Justin Chambers Opens Up About Sleep Disorder

"It's an issue that I've had for a while," the Grey's Anatomy star tells PEOPLE exclusively in his first interview since the incident. "It's a biological sleep disorder. Your mind keeps racing, and your body is tired. It wants to go to sleep, but it can't."

Chambers, 37, who has five children with his wife, Keisha, 38, says in the two months prior to checking in to UCLA, he was sleeping no more than an hour a week. "I got to my wit's end," he says.

For more on Chambers's family life, his return to Grey's, and his recovery, pick up the latest PEOPLE, on newsstands Friday.– Lisa Ingrassia